Muffler

ABSTRACT

A muffler including an inner pipe through which exhaust gas flows and communication portions formed in a peripheral wall of the inner pipe and including holes that communicate a gas flow path of the inner pipe with a muffling chamber. Each of the communication portions further include an inside deformation portion formed by deforming a portion of the peripheral wall toward the pipe inside, and having a downstream side end portion separated from the peripheral wall; and an outside deformation portion formed by deforming a portion of the peripheral wall adjacent to the downstream side of the inside deformation portion toward the pipe outside, and having a upstream side end portion separated from the peripheral wall. The holes are formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-062898, filed on Mar. 25, 2015, the disclosure of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to a muffler.

2. Related Art

Conventional mufflers are known in which small holes are formed in a peripheral wall of an inner pipe inserted into the interior of an outer shell, and an exhaust gas flow path at the inner pipe interior is placed in communication with a muffling chamber at the inner pipe exterior (for example, see Japanese Patent Application Laid-open (JP-A) No. 2002-47910).

However, in such conventional mufflers, fine particles, such as soot contained in the exhaust gas, are liable to collect at the edges of the small holes, and the small holes may be closed off by the fine particles. Such conventional mufflers are therefore liable to exhibit decreased exhaust muffling performance due to aging.

Hence, it is conceivable that a structure in which fine particles do not easily block the small holes could be applied; however, it would be undesirable for such structures to cause a large increase in resistance to ventilation of the exhaust gas.

SUMMARY

In consideration of the above circumstances, the present disclosure provides a muffler that makes it difficult for fine particles such as soot to block small holes placing the interior and exterior of an inner pipe in communication with each other, without a large attendant increase in ventilation resistance.

According to one aspect of the present disclosure, the muffler includes an inner pipe that is inserted into an outer shell interior and has an interior through which exhaust gas flows, and plural communication portions that are formed in a peripheral wall of the inner pipe, and that include holes that place an exhaust gas flow path of the inner pipe interior in communication with a muffling chamber at the inner pipe exterior. Each of the communication portions includes an inside deformation portion that is formed by deforming a portion of the peripheral wall toward the inner pipe inside and that has a gas flow downstream side end portion separated from the peripheral wall, and an outside deformation portion that is formed by deforming a portion of the peripheral wall adjacent to the gas flow downstream side of the inside deformation portion toward the inner pipe outside and that has a gas flow upstream side end portion separated from the peripheral wall. The hole is formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion.

The plural communication portions are formed in the peripheral wall of the inner pipe. The communication portions include the holes that place the exhaust gas flow path at the inner pipe interior in communication with the muffling chamber at the inner pipe exterior. Namely, the exhaust gas flow path at the inner pipe interior is placed in communication with the muffling chamber of the inner pipe exterior by the holes in the communication portions. Accordingly, sound waves caused by exhaust gas flowing through the exhaust gas pathway of the inner pipe interior pass through the holes, and are attenuated in the muffling chamber at the inner pipe exterior.

Moreover, the communication portions each include the inside deformation portion and the outside deformation portion. The inside deformation portion is formed by deforming a portion of the peripheral wall of the inner pipe toward the inner pipe interior, and is a portion at which the gas flow downstream side end portion is separated from the peripheral wall. The outside deformation portion is formed by deforming a portion of the peripheral wall adjacent to the gas flow downstream side of the inside deformation portion toward the inner pipe outside, and is a portion at which the gas flow upstream side end portion is separated from the peripheral wall. The hole of the communication portion is formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion that are both separated from the peripheral wall. The hole is therefore hidden by the inside deformation portion, as viewed from the upstream side of the communication portions inside the inner pipe. Accordingly, fine particles such as soot contained in the exhaust gas hit the inside deformation portion, and so the fine particles do not easily block the hole in the communication portion.

Moreover, as described above, the communication portions are each formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion. This enables the height of the inside deformation portion (amount of deformation toward the inner pipe inside) to be reduced while still securing the size of the hole, compared to a case in which the communication portion includes the inside deformation portion alone. Namely, increases in ventilation resistance can be prevented by providing the communication portions.

The profile of the hole may be substantially an ellipse with the direction of the major axis aligned with the peripheral direction of the inner pipe. In such a configuration, the profile of the hole is substantially an ellipse with the direction of the major axis of the substantially elliptical shape aligned with the peripheral direction of the inner pipe. This enables the height of the inside deformation portion (amount of deformation toward the inner pipe inside) to be set small while still securing the size of the hole. This further enables increases in ventilation resistance caused by the communication portion to be further suppressed.

Alternatively, the profile of the hole may be a substantially rectangular shape with a length direction aligned with the peripheral direction of the inner pipe. This configuration also enables the height of the inside deformation portion (amount of deformation toward the inner pipe inside) to be set small while still securing the size of the hole, and enables increases in ventilation resistance caused by the communication portion to be further suppressed.

The amount of deformation of the inside deformation portion toward the inner pipe inside may be less than the amount of deformation of the outside deformation portion toward the inner pipe outside.

In this muffler, the amount of deformation of the inside deformation portion toward the inner pipe inside is less than the amount of deformation of the outside deformation portion toward the inner pipe outside. This enables the height of the inside deformation portion (amount of deformation toward the inner pipe inside) to be set small while still securing the size of the hole, as long as the amount of deformation of the outside deformation portion toward the pipe outside is large. This further enables increases in ventilation resistance caused by the communication portion to be further suppressed.

The cross-section profiles of the inside deformation portion and the outside deformation portion taken along planes orthogonal to the inner pipe peripheral direction may be shaped approximately as arcs of a circle or an ellipse. Such a configuration enables numerous communication portions to be formed along the inner pipe length direction, and this enables muffling effects to be improved.

The inside deformation portion and the outside deformation portion may include a parallel portion that runs parallel to the direction of gas flow. In a muffler including the deformation portion having such a configuration, increases in ventilation resistance can be prevented due to the flow rectification action performed on the exhaust gas.

As explained above, the muffler of the present disclosure makes it difficult for fine particles such as soot to block small holes placing the interior and exterior of an inner pipe in communication with each other, without a large attendant increase in ventilation resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a perspective view of one communication portion of plural communication portions formed in an inner pipe peripheral wall of a muffler according to an exemplary embodiment, as viewed from the interior of an inner pipe (exhaust gas flow path);

FIG. 2 is a cross-section illustrating the communication portion illustrated in FIG. 1 in a state sectioned along line 2-2;

FIG. 3 is a cross-section illustrating the communication portion illustrated in FIG. 1 in a state sectioned along line 3-3;

FIG. 4 is a perspective view illustrating a muffler according to the present exemplary embodiment, in which an inner pipe is represented by a solid line, and an outer shell is represented by a double-dotted dashed line;

FIG. 5A to FIG. 5D relate to other exemplary embodiments; FIG. 5A is a cross-section corresponding to FIG. 2 illustrating a communication portion including a parallel portion; FIG. 5B is a cross-section corresponding to FIG. 2 illustrating a communication portion formed with a spherical surface shape; FIG. 5C is a cross-section corresponding to FIG. 3 illustrating a communication portion in which holes have substantially elliptical profiles; and FIG. 5D is a cross-section corresponding to FIG. 3 illustrating a communication portion in which holes have substantially rectangular shapes; and

FIG. 6 is a perspective view illustrating a muffler according to another exemplary embodiment, in which an inner pipe is represented by a solid line, and an outer shell is represented by a double-dotted dashed line.

DETAILED DESCRIPTION

Explanation follows regarding an exemplary embodiment of a muffler of the present disclosure, with reference to FIG. 1 to FIG. 4. As illustrated in FIG. 4, a muffler 10 is a muffler having a so-called straight structure in which a flow path for internally flowing exhaust gas is linear. The muffler 10 includes an outer shell 12 that configures an outermost wall of the muffler 10, and an inner pipe 14 that is inserted into the interior of the outer shell 12. The muffler 10 is disposed partway along a flow path that guides exhaust gas exhausted from an engine, not illustrated in the drawings, to the atmosphere.

The outer shell 12 includes a general portion 16 that has a tube shape having a wide diameter, narrowing diameter portions 18 that narrow in diameter from both longitudinal ends of the general portion 16 toward end portions 20 of the outer shell 12. Both of the end portions 20 are tubes having a narrow diameter (relative to the general portion 16) and which are joined to the inner pipe 14. The inner pipe 14 has a tube shape having a narrower diameter than the general portion 16 of the outer shell 12 and substantially the same diameter as both of the end portions 20 of the outer shell 12, and is disposed coaxially to the outer shell 12. The interior of the inner pipe 14 is an exhaust gas flow path 22 through which exhaust gas G flows, and a portion internal to the outer shell 12 and external to the inner pipe 14 is a muffler chamber 24. Plural communication portions 28 (see FIG. 1), described in detail below, are formed in a peripheral wall 26 of the inner pipe 14, namely, a portion indicated by the diagonal lines in FIG. 4. The communication portions 28 place the exhaust gas flow path 22 in communication with the muffler chamber 24. Sound caused by the exhaust gas G flowing through the exhaust gas flow path 22 is transmitted to the muffler chamber 24 by the communication portions 28, and is muffled in the muffler chamber 24. A sound absorbing material (not illustrated in the drawings), such as stainless steel wool or glass wool, is disposed in the muffler chamber 24.

Communication Portion

FIG. 1 illustrates one communication portion 28 of the plural communication portions 28 formed in the peripheral wall 26 of the inner pipe 14, as viewed from the interior of the inner pipe 14 (the exhaust gas flow path 22). In the respective drawings, the arrow F indicates the gas flow direction along the longitudinal length of the inner pipe 14, the arrow W indicates the width of the peripheral wall 26 of the inner pipe 14, and the arrow H indicates the height along the thickness direction of the peripheral wall 26. Hereafter, the gas flow direction (F) may be simply referred to as the “flow direction” or the “downstream side”, the width (W) of the peripheral wall 26 of the inner pipe 14 may be simply referred to as the “peripheral direction”, and the height (H) of the peripheral wall 26 may be simply referred to as the “inner pipe inside” or the “height direction”.

As illustrated in FIGS. 1 and 2, the communication portion 28 includes an inside deformation portion 30 formed by deforming a portion of the peripheral wall 26 toward the pipe inside direction (see dimension Hin), and an outside deformation portion 32 formed by deforming a portion of the peripheral wall 26 toward the pipe outside direction (see dimension Hout). The inside deformation portion 30 is formed contiguous to the peripheral wall 26 at a boundary portion 30A, but the inside deformation portion 30 is separated from the peripheral wall 26 at a downstream side end portion 30B. Moreover, the outside deformation portion 32 is formed contiguous to the peripheral wall 26 at a boundary portion 32A, but the outside deformation portion 32 is separated from the peripheral wall 26 at an upstream side end portion 32B.

The inside deformation portion 30 and the outside deformation portion 32 are provided adjacent to each other in the flow direction. A hole 34 penetrating through the peripheral wall 26 is thereby formed by the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32. The exhaust gas flow path 22 of the interior of the inner pipe 14 is in communication with the muffler chamber 24 of the exterior of the inner pipe 14 through this hole 34. Forming the hole 34 in this manner gives a configuration in which the hole 34 of the communication portion 28 is not visible from the upstream side of the communication portions 28 in the interior of the inner pipe 14. However, the hole 34 of the communication portion 28 is visible from the downstream side of the communication portions 28 in the interior of the inner pipe 14. Note that FIG. 1 is a diagram of the communication portion 28 viewed from the downstream side of the communication portions 28 in the interior of the inner pipe 14, and the hole 34 is illustrated in FIG. 1.

The inner pipe 14 having the communication portions 28 formed in the peripheral wall 26 in this manner can be, for example, manufactured by the following method. First, plural small notches, extending along the width direction, are formed in a rectangular shaped metal plate. Next, portions that face each other in the length direction across the notches are deformed at the surface side and rear face side of the plate by press working. Lastly, the rectangular shaped metal plate is wrapped to form a tube, and width direction end portions thereof are joined together. Due to this method, the inside deformation portion 30 has a louver form which projects toward the pipe inside direction and opens at the downstream side. Moreover, the outside deformation portion 32 has a louver form which projects toward the pipe outside direction and opens at the upstream side.

The inside deformation portion 30 is formed with a curved face convex toward the pipe inside direction. Namely, as illustrated in FIG. 2, at the peripheral direction center of a cross-section profile sectioned along a plane orthogonal to the peripheral direction, the inside deformation portion 30 is substantially parallel to the gas flow direction in the vicinity of the downstream side end portion 30B (hole 34), and an angle of the inside deformation portion 30 with respect to the gas flow direction increases on progression away from the downstream side end portion 30B (hole 34) toward the upstream side. Moreover, as illustrated in FIG. 3, the inside deformation portion 30 is parallel to the peripheral direction at the peripheral direction center, and has an angle with respect to the peripheral direction that increases toward the peripheral direction outside, as viewed from the downstream side. Although FIG. 3 illustrates the downstream side end portion 30B of the inside deformation portion 30, when the inside deformation portion 30 is sectioned along any plane orthogonal to the direction of gas flow, the inside deformation portion 30 is parallel to the peripheral direction at the peripheral direction center, and has an angle with respect to the peripheral direction that increases on progression toward the peripheral direction outside.

The outside deformation portion 32 is formed with a curved face convex toward the pipe outside direction. Namely, as illustrated in FIG. 2, in a cross-section profile at the peripheral direction center of the outside deformation portion 32 sectioned along a plane orthogonal to the peripheral direction, the vicinity of the upstream side end portion 32B (hole 34) is substantially parallel to the direction of gas flow, and an angle of the outside deformation portion 32 with respect to the gas flow direction increases from the upstream side end portion 32B (hole 34) toward the downstream side. Moreover, as indicated by the double-dotted dashed lines in FIG. 3, as viewed from the downstream side, the outside deformation portion 32 is parallel to the peripheral direction at the peripheral direction center, and has an angle with respect to the peripheral direction that increases toward the peripheral direction outside. Although the double-dotted dashed lines in FIG. 3 indicate the upstream side end portion 32B of the outside deformation portion 32, when the outside deformation portion 32 is sectioned along any plane orthogonal to the direction of gas flow, the outside deformation portion 32 is parallel to the peripheral direction at the peripheral direction center, and has an angle with respect to the peripheral direction that increases toward the peripheral direction outside. In other words, the communication portion 28 that includes the inside deformation portion 30 and the outside deformation portion 32 is shaped such that the downstream side half having a dome shape, formed so as to protrude toward the pipe inside direction, is inverted toward the pipe outside.

As illustrated in FIG. 3, the hole 34 of the communication portion 28 is a circular shape substantially orthogonal to the direction of gas flow. Namely, as illustrated in FIG. 2, the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32 both form substantially right angles with respect to the peripheral wall 26. Moreover, the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32 are both formed as semicircular shapes.

As illustrated in FIG. 2, an angle is formed between the inside deformation portion 30 and the peripheral wall 26 at the boundary portion 30A at which the inside deformation portion 30 connects to the peripheral wall 26. Namely, the boundary portion 30A has a shape in which the peripheral wall 26 rises rapidly at the boundary portion 30A, without there being a gentle curved surface. Moreover, an angle is formed between the outside deformation portion 32 and the peripheral wall 26 even at the boundary portion 32A at which the outside deformation portion 32 connects to the peripheral wall 26. Namely, the boundary portion 32A has a shape in which the peripheral wall 26 rises rapidly at the boundary portion 32A, without there being a gently curved surface.

As illustrated in FIG. 2, the dimension Lin of the inside deformation portion 30 along the direction of gas flow is formed larger than the dimension Hin of the inside deformation portion 30 along the pipe inside direction. Moreover, the dimension Lout of the outside deformation portion 32 along the direction of gas flow is formed larger than the dimension Hout of the outside deformation portion 32 along the pipe outside direction. Note that in the present exemplary embodiment, Lin and Lout are formed substantially equal to each other, and Hin and Hout are formed substantially equal to each other.

Operation and Effects

Next, explanation follows regarding the operation and effects of the muffler 10 of the present exemplary embodiment.

In the muffler 10 of the present exemplary embodiment, the peripheral wall 26 of inner pipe 14 is formed with the plural communication portions 28, each including the hole 34, which places the exhaust gas flow path 22 at the pipe inside in communication with the muffler chamber 24 at the pipe outside. Sound waves caused by exhaust gas flowing through the exhaust gas flow path 22 therefore enter the muffler chamber 24 via the hole 34, and are attenuated by the noise absorbing effect of the glass wool or stainless steel wool of the muffler chamber 24.

The communication portion 28 of the present exemplary embodiment also includes the inside deformation portion 30 and the outside deformation portion 32. The inside deformation portion 30 is formed by deforming a portion of the peripheral wall 26 of the inner pipe 14 toward the inner pipe inside, and is a portion at which the gas flow downstream side end portion 30B has separated from the peripheral wall 26. The outside deformation portion 32 is formed by deforming the portion of the peripheral wall 26 adjacent to the inside deformation portion 30 at the gas flow downstream side toward the inner pipe outside, and is a portion at which the gas flow upstream side end portion 32B has separated from the peripheral wall 26. The hole 34 of the communication portion 28 is formed by the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32 that are both separated from the peripheral wall 26. The hole 34 is therefore hidden by the inside deformation portion 30, as viewed from the upstream side of the communication portions 28 inside the inner pipe 14. Accordingly, fine particles such as soot are prevented from blocking the hole 34, since fine particles such as soot contained in the exhaust gas G hit the inside deformation portion 30. Thus, the muffler 10 is particularly well suited to a vehicle equipped with an engine in which soot is liable to be contained in exhaust gas, such as a direct-injection engine.

Moreover, in the present exemplary embodiment, as explained above, the hole 34 of the communication portion 28 is formed by the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32. This enables the height Hin of the inside deformation portion 30 (amount of deformation toward the inner pipe inside) to be reduced while still securing the size of the hole 34, compared to a case in which the communication portion 28 includes the inside deformation portion 30 alone. Namely, increases in ventilation resistance can be prevented by providing the communication portions 28. Namely, ventilation resistance for the exhaust gas G can be lowered in the muffler 10, while still securing muffling performance.

Moreover, the outside deformation portion 32 of the present exemplary embodiment fulfils the role of fixing the position where the glass wool or stainless steel wool is disposed at the outside of the inner pipe 14. This prevents positional displacement of sound absorbing material, such as glass wool or stainless steel wool, in the muffler 10.

Moreover, the communication portions 28 of the present exemplary embodiment can be manufactured by cutting a notch in the peripheral wall 26 of the inner pipe 14, and then press working. Accordingly, no waste is generated by cutting the peripheral wall 26 during manufacture. Moreover, burrs (protuberances), not illustrated in the drawings, are generated during manufacture of the communication portions 28 at the downstream side end portion 30B of the inside deformation portion 30 and the upstream side end portion 32B of the outside deformation portion 32; however, these burrs are formed facing the inside direction of the hole 34. Accordingly, the burrs do not cause ventilation resistance for the exhaust gas G Moreover, the burrs do not damage the glass wool or stainless steel wool disposed at the outside of the inner pipe 14.

Moreover, it is conceivable that the turbulent flow in the exhaust gas G flowing through the exhaust gas flow path 22 would be caused by the inside deformation portion 30 being deformed toward the inner pipe inside. However, in the present exemplary embodiment, turbulent flow is suppressed from being generated in the exhaust gas G since the inside deformation portion 30 is formed with a curved face convex toward the pipe inside direction.

Supplementary Explanation of Above Exemplary Embodiment

Note that, in the exemplary embodiment described above, the cross-section profiles, given by sectioning the inside deformation portion 30 and the outside deformation portion 32 along a plane orthogonal to the peripheral direction (the cross-section profile illustrated in FIG. 2), are formed so as to be shaped approximately as arcs of an ellipse; however, the “communication portion” of the present disclosure is not limited thereto. For example, a communication portion 128 or a communication portion 228, having cross-section profiles like those illustrated in FIG. 5A and FIG. 5B, may be employed.

In the communication portion 128 illustrated in FIG. 5A, an inside deformation portion 130 is configured including a parallel portion 130C parallel to the flow direction. An end portion at the downstream side of the parallel portion 130C configures a downstream side end portion 130B of the inside deformation portion 130. Moreover, an outside deformation portion 132 includes a parallel portion 132C parallel to the flow direction. An end portion at the upstream side of the parallel portion 132C includes an upstream side end portion 132B of the outside deformation portion 132. A flow rectification action is accordingly performed on the exhaust gas and an increase in ventilation resistance in the muffler provided with the communication portion 128 is suppressed. Moreover, in the communication portion 128, the peripheral wall 26 and boundary portions 130A, 132A are formed as gently curved faces.

A cross-section profile of the communication portion 228, illustrated in FIG. 5B, sectioned along a plane orthogonal to the peripheral direction forms a circular arc shape in the communication portion 228. Namely, an inside deformation portion 230 and an outside deformation portion 232 are each shaped as one quarter of a divided sphere. Thus, numerous communication portions 228 can be formed along the inner pipe length direction in the muffler provided with the communication portion 228.

Moreover, in the above exemplary embodiment, the hole 34 of the communication portion 28 is a circular shape as viewed along the downstream direction (see FIG. 3); however, the present disclosure is not limited thereto. For example, a communication portion 328 or a communication 428 having holes 34 as illustrated in FIG. 5C and FIG. 5D may be employed.

In the communication portion 328 illustrated in FIG. 5C, the hole 34 has a substantially elliptical profile, with a height dimension smaller than the width dimension thereof. Namely, the hole 34 has a substantially elliptical profile, with the direction of the major axis of the substantially elliptical profile aligned with the peripheral direction of the peripheral wall 26 of the inner pipe 14. In this communication portion 328, while still securing the size of the holes, the ventilation resistance of the exhaust gas G can be lowered while securing muffling performance, since the height dimension Hin of the inside deformation portion 30 can be formed smaller.

The hole 34 is formed with a substantially rectangular profile in the communication 428 illustrated in FIG. 5D. A muffler including the communication 428 is included in the present disclosure.

Moreover, although the height dimension Hin of the inside deformation portion 30 and the height dimension Hout of the outside deformation portion 32 are set substantially equal to each other in the above exemplary embodiment, the present disclosure is not limited thereto. For example, the height dimension Hin of the inside deformation portion 30 may be set smaller than the height dimension Hout of the outside deformation portion 32. In such cases, the height of the inside deformation portion 30 can be formed smaller while securing the size of the hole, thereby enabling increases in ventilation resistance to be further suppressed.

Moreover, although the muffler 10 is a so-called straight type muffler in the above exemplary embodiment, the “muffler” of the present disclosure is not limited thereto. For example, as illustrated in FIG. 6, a muffler 510 that lacks a straight structure may be employed. In the muffler 510, the interior of an outer shell 512 is divided into a first muffling chamber 524A, a second muffling chamber 524B, and a third muffling chamber 524C, by a first separator 540 and a second separator 542. As an explanation of flow of the exhaust gas G in this muffler 510, first, the exhaust gas G flows through the interior of an introducing pipe 514A, and is introduced into the third muffling chamber 524C. Next, the exhaust gas G introduced into the third muffling chamber 524C flows through the interior of an intermediate pipe 514B, and is introduced into the first muffling chamber 524A. Finally, the exhaust gas G introduced into the first muffling chamber 524A flows through the interior of a lead-out pipe 514C and is led out to the exterior of the muffler 510. Namely, the flow direction in which the exhaust gas G flows through the interior is clear in each out of the introducing pipe 514A, the intermediate pipe 514B, and the outlet pipe 514C.

In the muffler 510 formed in this manner, communication portions may be formed in the peripheral walls of all or some out of the introducing pipe 514A, the intermediate pipe 514B, and the outlet pipe 514C (the portions indicated by the diagonal lines in FIG. 6). Namely, the inner pipe provided with the muffler of the present disclosure is one in which exhaust gas flows internally in a specific direction when the engine is running with a muffling chamber formed outside, and the specific structure of the muffler 10 is not particularly limited.

Moreover, although a sound absorbing material such as glass wool or stainless steel wool is disposed in the interior of the muffling chamber in the above exemplary embodiment, the “muffling chamber” of the present disclosure is not limited thereto. The interior of the muffling chamber may be empty. Moreover, although the muffler chamber 24 is formed by the outer shell 12 and the inner pipe 14 in the above exemplary embodiment, the “muffling chamber” of the present disclosure is not limited thereto. “Muffling chambers” of the present disclosure include any chambers formed at the exterior of an inner pipe. 

What is claimed is:
 1. A muffler comprising: an inner pipe which has an interior through which exhaust gas flows; and a plurality of communication portions formed in a peripheral wall of the inner pipe, each of the communication portions including holes that place an exhaust gas flow path of the inner pipe interior in communication with a muffling chamber at the inner pipe exterior, an inside deformation portion formed by deforming a portion of the peripheral wall toward the inner pipe inside, and that has a gas flow downstream side end portion separated from the peripheral wall, and an outside deformation portion formed by deforming a portion of the peripheral wall adjacent to the gas flow downstream side of the inside deformation portion toward the inner pipe outside, and that has a gas flow upstream side end portion separated from the peripheral wall; wherein the holes are formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion.
 2. The muffler of claim 1, wherein the profile of the holes is substantially an ellipse with the direction of the major axis aligned with the peripheral direction of the inner pipe.
 3. The muffler of claim 1, wherein the profile of the holes is a substantially rectangular shape with a length direction aligned with the peripheral direction of the inner pipe.
 4. The muffler of claim 1, wherein the amount of deformation of the inside deformation portion toward the inner pipe inside is less than the amount of deformation of the outside deformation portion toward the inner pipe outside.
 5. The muffler of claim 1, wherein the cross-section profiles of the inside deformation portion and the outside deformation portion taken along planes orthogonal to the inner pipe peripheral direction are shaped approximately as arcs of a circle or an ellipse.
 6. The muffler of claim 1, wherein the inside deformation portion and the outside deformation portion include a parallel portion that runs parallel to the direction of gas flow.
 7. The muffler of claim 1, further comprising: an outer shell; wherein the inner pipe is provided within an interior of the outer shell.
 8. A muffler comprising: an outer shell including a plurality of muffling chambers; a plurality of inner pipes, each inner pipe having an interior through which exhaust gas flows, the plurality of inner pipes provided transverse to the muffling chambers within an interior of the outer shell; and a plurality of communication portions formed in a peripheral wall of at least one of the inner pipes, each of the communication portions including holes that place an exhaust gas flow path of the inner pipe interior in communication with a muffling chamber at the inner pipe exterior, an inside deformation portion formed by deforming a portion of the peripheral wall toward the inner pipe inside, and that has a gas flow downstream side end portion separated from the peripheral wall, and an outside deformation portion formed by deforming a portion of the peripheral wall adjacent to the gas flow downstream side of the inside deformation portion toward the inner pipe outside, and that has a gas flow upstream side end portion separated from the peripheral wall; wherein the holes are formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion.
 9. An inner pipe of a muffler comprising: a plurality of communication portions formed in a peripheral wall of the inner pipe, each of the communication portions including holes that place an exhaust gas flow path of the inner pipe interior in communication with a muffling chamber at the inner pipe exterior, an inside deformation portion formed by deforming a portion of the peripheral wall toward the inner pipe inside, and that has a gas flow downstream side end portion separated from the peripheral wall, and an outside deformation portion formed by deforming a portion of the peripheral wall adjacent to the gas flow downstream side of the inside deformation portion toward the inner pipe outside, and that has a gas flow upstream side end portion separated from the peripheral wall; wherein the holes are formed by the downstream side end portion of the inside deformation portion and the upstream side end portion of the outside deformation portion. 